Cell spheroids as a versatile research platform: formation mechanisms, high throughput production, characterization and applications.

Three-dimensional (3D) cell culture has tremendous advantages to closely mimic thein vivoarchitecture and microenvironment of healthy tissue and organs, as well as of solid tumors. Spheroids are currently the most attractive 3D model to produce uniform reproducible cell structures as well as a potential basis for engineering large tissues and complex organs. In this review we discuss, from an engineering perspective, processes to obtain uniform 3D cell spheroids, comparing dynamic and static cultures and considering aspects such as mass transfer and shear stress. In addition, computational and mathematical modeling of complex cell spheroid systems are discussed. The non-cell-adhesive hydrogel-based method and dynamic cell culture in bioreactors are focused in detail and the myriad of developed spheroid characterization techniques is presented. The main bottlenecks and weaknesses are discussed, especially regarding the analysis of morphological parameters, cell quantification and viability, gene expression profiles, metabolic behavior and high-content analysis. Finally, a vast set of applications of spheroids as tools forin vitrostudy model systems is examined, including drug screening, tissue formation, pathologies development, tissue engineering and biofabrication, 3D bioprinting and microfluidics, together with their use in high-throughput platforms.

DROSOPHILA S2 cell culture in a WAVE Bioreactor: potential for scaling up the production of the recombinant rabies virus glycoprotein.

The transmembrane rabies virus glycoprotein (RVGP) is the main antigen of vaccine formulations used around the world to prevent rabies, the most lethal preventable infectious disease known. The objective of this work was to evaluate the potential of a bioreactor using wave-induced agitation in the initial steps of scaling up the rRVGP production process by a Drosophila melanogaster S2 cell line to produce rRVGP in sufficient quantities for immunization and characterization studies. Taking advantage of some remarkable features recognized in Drosophila S2 cells for scaling the culture process, a robust recombinant lineage (S2MtRVGPH-His) engineered by our group for the expression of rRVGP using a copper-inducible promoter was used in the bioreactor cultures. The WAVE Bioreactor was chosen because it represents an innovative approach to the cultivation of animal cells using single-use technology. For that purpose, we firstly established a procedure for culturing the S2MtRVGPH-His lineage in 100 mL Schott flasks. Using an inoculum of 5 × 105 cells/mL in culture medium (Sf900-III) induced with solution of CuSO4 (0.7 mM) and a convenient pH range (6.2-7.0), optimal parameter values such as time of induction (72 h) and temperature (28 °C) to increase rRVGP production could be defined. This procedure was reproduced in culture experiments conducted in a WAVE Bioreactor™ 2/10 using a 2 L Cellbag. The results in Schott flasks and in WAVE Bioreactor™ were very similar, yielding a maximum titer of rRVGP above of 1 mg.L-1. The immunization study showed that the rRVGP produced in the bioreactor was of high immunogenic quality.

Log law of the wall revisited in Taylor-Couette flows at intermediate Reynolds numbers.

We provide Reynolds averaged azimuthal velocity profiles, measured in a Taylor-Couette system in turbulent flow, at medium Reynolds (7800 < Re < 18000) number with particle image velocimetry technique. We find that in the wall regions, close to the inner and outer cylinders, the azimuthal velocity profile reveals a significant deviation from classical logarithmic law. In order to propose a new law of the wall, the profile of turbulent mixing length was estimated from data processing; it was shown to behave nonlinearly with the radial wall distance. Based on this turbulent mixing length expression, a law of the wall was proposed for the Reynolds averaged azimuthal velocity, derived from momentum balance and validated by comparison to different data. In addition, the profile of viscous dissipation rate was investigated and compared to the global power needed to maintain the inner cylinder in rotation.

Transient expression of rabies virus glycoprotein (RVGP) in Drosophila melanogaster Schneider 2 (S2) cells.

The transient transfection process has been developed to allow rapid production of recombinant proteins. In this paper, we describe the transient expression of recombinant rabies virus glycoprotein (RVGP) in Drosophila melanogaster Schneider 2 (S2) cells. Different cell transfection reagents were evaluated, together with the effects of different cell cultivation procedures on RVGP expression. Yields of RVGP in the range 50-90ng/10(7) cells were obtained in multi-well plate transfection experiments, where it was observed that RVGP expression was linked to the DNA concentration. RVGP expression was 1.3 times higher using 10µg rather than 5µg of DNA. Inhibition of RVGP expression was observed at higher concentrations of DNA, with DNA concentrations above 15µg decreasing RVGP expression 1.5-fold for cells transfected with polyethylenimine (PEI) and 1.6-fold for cells transfected with cationic lipid. The results of shake flask transfection indicated that S2 cells were more effectively transfected in suspension than under static conditions. RVGP yields of 182.2ng/10(7) cells (PEI), 201ng/10(7) cells (calcium phosphate), and 215ng/10(7) cells (cationic lipid) were obtained for S2 cell suspension cultures. The highest volumetric RVGP concentration (309ng/mL) was found for cells transfected with cationic lipid. This value was 1.21 and 1.16 times higher, respectively, than for cells transfected with PEI (253.4ng/mL) and calcium phosphate (237.2ng/mL). There was little effect of transfection on the kinetics of cell growth, with growth rates of 1.12 and 1.19d(-1) for transfected and control cells, respectively. In spinner flasks, the expression of RVGP was 150 and 138ng/10(7) cells for transfection using PEI and calcium phosphate, respectively. A comparison of the different transfection reagents (calcium phosphate, cationic lipid, and cationic polymer) showed no significant differences in RVGP expression when shake flasks were used. Overall, the data indicated that transient expression in D. melanogaster S2 cells is a practical way of synthesizing RVGP for use in structural and functional studies.

Recombinant rabies virus glycoprotein synthesis in bioreactor by transfected Drosophila melanogaster S2 cells carrying a constitutive or an inducible promoter.

S2 cell populations (S2AcRVGP2K and S2MtRVGP-Hy) were selected after transfection of gene expression vectors carrying the cDNA encoding the rabies virus glycoprotein (RVGP) gene under the control of the constitutive (actin) or inductive (metallothionein) promoters. These cell populations were cultivated in a 1L bioreactor mimicking a large scale bioprocess. Cell cultures were carried out at 90 rpm and monitored/controlled for temperature (28 degrees C) and dissolved oxygen (10 or 50% air saturation). Cell growth attained approximately 1.5-3 x 10(7)cells/mL after 3-4 days of cultivation. The constitutive synthesis of RVGP in S2AcRVGP2K cells led to values of 0.76 microg/10(7) cells at day 4 of culture. The RVGP synthesis in S2MtRVGP-Hy cell fraction increased upon CuSO(4) induction attaining specific productivities of 1.5-2 microg/10(7) cells at days 4-5. RVGP values in supernatant as a result of cell lysis were always very low (<0.2 microg/mL) indicating good integrity of cells in culture. Overall the RVGP productivity was of 1.5-3mg/L. Our data showed an important influence of dissolved oxygen on RVGP synthesis allowing a higher and sustained productivity by S2MtRVGP-Hy cells when cultivated with a DO of 10% air saturation. The RVGP productivity in bioreactors shown here mirrors those previously observed for T-flasks and shaker bottles and allow the preparation of the large RVGP quantities required for studies of structure and function.

Bioreactor culture of recombinant Drosophila melanogaster S2 cells: characterization of metabolic features related to cell growth and production of the rabies virus glycoprotein.

Although several reports have been published on recombinant protein expression using Drosophila cells, information on their metabolism and growth in vitro is relatively scarce. In the present study, we have analyzed the growth and metabolism of transfected S2 cells (S2AcRVGP) in bioreactor cultures with serum-free medium Sf900 II, to evaluate its potential for mass production of a rabies virus glycoprotein (RVGP). Cells were cultured in a 3 l-stirred-tank bioreactor at 28 degrees C with pH controlled at 6.2 and dissolved oxygen at 50% air saturation. The cells attained a specific growth rate and maximum cell density as high as 0.084 h(-1) and 2.3 x 10(7 )cell ml(-1), respectively. The main substrates consumed during this rapid growth phase were glucose, glutamine and proline. An atypical accumulation of ammonia and alanine was observed in the culture medium, up to 62 mM and 47 mM, respectively, but lactate was produced in low levels. After exhaustion of glutamine and proline as energy sources, alanine was consumed and production of ammonia increased. The production of recombinant RVGP reached concentrations as high as 178 mug l(-1). Premature exhaustion of glutamine, serine and cysteine could be related to degradation of the recombinant glycoprotein. In general, the results demonstrated that S2AcRVGP can be considered an effective vehicle for large-scale recombinant glycoprotein expression and that several critical factors of the bioprocess could be optimized to increase the quality and productivity of the RVGP.

Bioreactor culture of recombinant Drosophila melanogaster S2 cells: characterization of metabolic features related to cell growth and production of the rabies virus glycoprotein

Although several reports have been published on recombinant protein expression using Drosophila cells, information on their metabolism and growth in vitro is relatively scarce. In the present study, we have analyzed the growth and metabolism of transfected S2 cells (S2AcRVGP) in bioreactor cultures with serum-free medium Sf900 II, to evaluate its potential for mass production of a rabies virus glycoprotein (RVGP). Cells were cultured in a 3 l-stirred-tank bioreactor at 28 ‹C with pH controlled at 6.2 and dissolved oxygen at 50% air saturation. The cells attained a specific growth rate and maximum cell density as high as 0.084 h−1 and 2.3 ~ 107 cell ml−1, respectively. The main substrates consumed during this rapid growth phase were glucose, glutamine and proline. An atypical accumulation of ammonia and alanine was observed in the culture medium, up to 62 mM and 47 mM, respectively, but lactate was produced in low levels. After exhaustion of glutamine and proline as energy sources, alanine was consumed and production of ammonia increased. The production of recombinant RVGP reached concentrations as high as 178 ƒÊg l−1. Premature exhaustion of glutamine, serine and cysteine could be related to degradation of the recombinant glycoprotein. In general, the results demonstrated that S2AcRVGP can be considered an effective vehicle for large-scale recombinant glycoprotein expression and that several critical factors of the bioprocess could be optimized to increase the quality and productivity of the RVGP.

Performance evaluation of CHO-K1 cell in culture medium supplemented with hemolymph

Desenvolvimento de meios de cultura isentos de soro fetal bovino (SFB) é uma das grandes prioridades de pesquisa em desenvolvimento de processos com célula animal. O objetivo do presente trabalho foi realizar uma análise do potencial de uso da hemolinfa como suplemento do meio utilizado no cultivo da célula animal ancorante CHO-K1. Para isso, foi adicionado 1% v/v de extrato de hemolinfa ao meio DMEM contendo 10% v/v de SFB e 1,0 ou 4,5 g/L de glicose. O cultivo foi realizado em frascos tipo spinner em um ambiente de 10% v/v de CO2, a 37ºC, utilizando o microcarregador Cytodex 1. Comparando os resultados obtidos no ensaio com hemolinfa com um sem hemolinfa pode-se notar uma influência positiva da hemolinfa no cultivo, já que o ensaio com hemolinfa apresentou uma concentração máxima de células 52% maior e uma produtividade máxima de até 40% maior.